Traveling wave tube



A ril- 16, 1957 Filed July 22, 1949 J. H. JONKER 2,789,247

TRAVELING WAVE TUBE 2 Sheets-Sheet 1 I/IVVEATO/P J'O/M/V/VEJ 1005M.Willi/A fan A275 April 6, 1957 J. H. JONKER 2,789,247

TRAVELING WAVE TUBE Filed July 22, 1949 2 Sheets -Sheet 2 &

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2,789,247 Patented Apr. 16, 1957 TRAVELING WAVE TUBE Johannes LodewijkHendrik Jonker, Eindhoven, Netherlands, assignor, by mesne assignments,to North American Philips Company, Inc., New York, N. Y., a corporationof Delaware This invention relates to electron discharge tubes forgenerating, amplifying or modulating waves having a wave-length of a fewcentimetres or less, in which device an electron-beam interacts with acoiled conductor.

Electron discharge tubes of the above type are also known as travellingwave tubes. In such tubes the electron beam is modulated by applying anA. C. voltage to the beginning of the coil. This A. C. voltage producesdensity modulation of the beam and the resultant maxima and minimainduce voltages in the coiled conductor, these voltages developing intoa travelling wave. Owing to the interaction between the coil and thebeam, an amplified voltage can be taken from the end of the coil.

If the wavelength of the electrical oscillations is small, it isditficult to obtain sufficient interaction between the coil and theelectron-beam because when the length of one turn becomes comparable tohalf the wave-length, the interaction decreases markedly. The use oflong coils to ensure sufiicient interaction is objectionable for shortwaves.

According to the present invention, an electron discharge tube, of thetravelling wave tube type, for generating, amplifying or modulatingwaves having a wavelength of a few centimetres or less, is characterizedin that the electron-beam travels not only at the inner side but also atthe outer side of at least one coil. Thus it is ensured that theinteraction between the electron beam and a coil of a given size ismaterially increased. Moreover, with a coil of any given size, thecross-section of the beam may be greater, so that the beam is adapted tocarry more current. Furthermore the lower current density permitssimpler focussing. Since, in this event, coils of a very small diametercan be used, shorter Waves can be generated or amplified or modulated.

In a particular form of a tube according to the invention, a pluralityof equal and similar coils, that is to say, coils of equal length,diameter and pitch, are stretched between two perforated plates, forexample rings, which are housed perpendicularly in a preferablyconductive cylinder. The spacing between the coils is preferablyapproximately 1% to 2 times the diameter of the coils. Furthermore, thecoils are arranged in a manner such that the turns are located as muchas possible adjacent each other in a section at right angles to the axisof the beam.

Alternatively, only one coil may be provided between two rings in theconductive cylinder. This, also, yields satisfactory results.

At its end, the cylindrical conductive tube containing the coils may beprovided with means for radiating the resultant energy or it may beinserted directly into a wave-guide.

In order that the invention may be more clearly understood and readilycarried into efiect, two examples will now be described with referenceto the accompanying drawings, of which:

Fig. 1 represents an electron discharge tube having a single coil andFigs. 2 and 3 are {a longitudinal view and a cross-section respectivelyof the electrode system of a tube having a plurality of coils.

In Fig. 1, the reference numeral 1 designates the base of a tube, madeof sintered powdered glass and in which a number of pins 2 are provided.An incandescent cathode 3 having a heater coil .4 is secured tothecentral pins 2. Over the incandescent cathode 3, a nickel cup 5 isprovided at a distance of approximately 1 mm. from the cathode, whichcup is provided with a central aperture having a diameter ofapproximately 1.5 mm. In front of the nickel cup 5 is provided acylindrical tube 6 of an iron-nickel alloy having an internal diameterof 3 ms. and a length of approximately 10 mms. A copper tube 8 has itslower peripheral edge tapered and is sealed toa glass bulb 7,'which isin turn sealed to the base 1. Two insulating, ceramic plates 9, eachhaving an aperture of diameter 3 mms., are arranged normally to the axisof tube 8. Between these plates, a tungsten coil 12, i. e., a helicalwire conductor, is stretched. This coil has a pitch of 0.3 mm. and iswound on a mandrel 1 mm. thick, the thickness of the wire being 0.1 mm.The tube 8 is closed at its end in a vacuum tight manner by means of aglass plug 10, which also serves as an energy outlet for the tube. Afocussing coil 11 is arranged coaxially with the tube 8. Duringoperation of the tube, the electrode 5 has a voltage of approximately 0v. and the tubes 6 and 8 attain a potential of 1000 v. and 2000 v. to4000 v., respectively. The focussing magnetic field has a value of 200gauss. As will be evident from the foregoing description, the elements3, 5, 6 and 8 cooperate to produce and project an electron beam throughthe cylinder 8 such that part of the beam passes along the inside andanother part along the outside of the coil 12.

In Figs. 2 and 3, the parts corresponding to those shown in Fig. 1 havethe same reference numerals. Be tween the plates 9, six coils 12 arestretched, all having the same pitch and the same diameter as each otherand wound alternately leftand right-handed. The spacing between thecoils is 1 /2 to 2 times the diameter of the coils in order that no deadspaces exist at which velocity modulation of the beam fails to occur.The alternate directions of winding of the coils enables the productionof an intense modulating field without deflecting the beam.

What I claim is:

1. A travelling wave tube comprising an evacuated envelope, a helicalwire conductor for guiding high-frequency electromagnetic waves disposedwithin said envelope and having a central axis and defining a dischargespace of given cross-sectional area at right angles to said axis throughsaid helical conductor, and means for producing and projecting a beam ofelectrons of solid crosssectional area greater than said givencross-sectional area in the direction of the axis of said conductor,whereby a portion of the beam passes along the inside of the helicalconductor and a portion passes around the outside of the entireconductor.

2. A travelling wave tube comprising an evacuated envelope including aconductive cylinder having a longitudinal axis, a helical wire conductorfor guiding highfrequency electromagnetic waves disposed coaxiallywithin said cylinder and spaced therefrom, said helical conductor havinga central axis and defining a discharge space of given cross-sectionalarea at right angles to its axis through said helical conductor, andmeans for producing and projecting a beam of electrons of solidcrosssectional area greater than said given cross-sectional area in thedirection of the axis of said conductor, whereby a portion of the beampasses along the inside of and a portion around the outside of theentire conductor.

3. A travelling wave tube comprising an evacuated envelope, a pluralityof spaced, parallel, helical wire conductors for guiding high-frequencyelectromagnetic waves a '2 t V a disposed within said envelope anddefining a discharge 7 space of given cross-sectional area at rightangles to said conductors, and means for producing and projecting a beamof electrons of solid cross-sectional area greater than s'a'id'givencross-sectional area in the direction of saidconductors, whereby aportion ofthe beam passes through and a'portion around the outside ofall of the conductors.

4. A travelling wave tube comprising an evacuated envelope including aconductive cylinder having a longitudinal axis, a plurality, of spaced,parallel, helical wire conductors for guiding high-frequencyelectromagnetic waves disposed lengthwise within said cylinder anddefining a discharge space of given cross-sectional area at right anglesto said conductors, said conductors being of substantially equal length,diameter and pitch, and means for producing and projecting a beam ofelectrons of solid cross-sectional area greater than said givencross-sectional area in the direction of said conductors, whereby a portion of the beam passes through and a portion around the outside of allof the conductors.

5. A travelling wave tube as claimed in claim 4 in which the conductorsare spaced apart a distance of approximately twice the said conductordiameter, a portion of said helical conductors being right-hand woundand the remainder of said conductors being left-hand Wound.

References Cited in the file oftthis patent UNITED STATES PATENTS2,064,469 Haeff Dec. 15, 1936 2,211,859 Percival Aug. 20, 1940 2,300,052Lindenblad Oct. 27, 1942 2,578,434 Lindenblad Dec. 11, 1951 2,641,730Touraton et al. June 9, 1953 2,643,353 Dewey a June 23, 1953

